A twin scroll turbocharger, which avoids the exhaust interference caused by a plurality of cylinders of an engine and improves the rotation efficiency of a turbine rotor by effectively using a pulse effect of an exhaust pulse, is known as a turbocharger that is mounted on a vehicle.
FIG. 7 is a schematic view of an engine including such a twin scroll turbocharger. As shown in FIG. 7, an engine 100 including a twin scroll turbocharger 130 includes, for example, four cylinders 10a, 10b, 10c, and 10d and phases of crank angles of these cylinders 10a to 10d are shifted from each other by, for example, 180□. Among these four cylinders, the cylinders 10a and 10d are connected to a first exhaust manifold 16 and the cylinders 10b and 10c are connected to a second exhaust manifold 18. The phases of the crank angles of the cylinders 10a and 10d are shifted from each other by, for example, 360□, so that the respective exhaust pulses of the cylinders 10a and 10d do not interfere with each other. Likewise, the phases of the crank angles of the cylinders 10b and 10c are shifted from each other by, for example, 360□, so that the respective exhaust pulses of the cylinders 10b and 10c do not interfere with each other.
The first exhaust manifold 16 is connected to an exhaust gas passage (front-side passage 122) formed in a turbine housing 132, so that exhaust gas discharged from the cylinders 10a and 10d is introduced to a turbine rotor 140 accommodated in the turbine housing 132 through the front-side passage 122. Likewise, the second exhaust manifold 18 is connected to an exhaust gas passage (rear-side passage 124) formed in the turbine housing 132, so that exhaust gas discharged from the cylinders 10b and 10c is introduced to the turbine rotor 140 accommodated in the turbine housing 132 through the rear-side passage 124. When a rotor blade 142 is rotated by the introduced exhaust gas, the turbine rotor 140 and a turbine shaft 36 supporting the turbine rotor 140 are rotated and a compressor rotor 34 supported by the turbine shaft 136 is rotated. Accordingly, compressed air is supplied to each of the cylinders 10a to 10d through an intake pipe 14 and an intake manifold 12. The exhaust gas, which has rotated the turbine rotor 140, is discharged to the outside of the engine 100 from an exhaust pipe 20.
The twin scroll turbocharger 130 needs to be designed so that the flow-through abilities of the two exhaust gas passages 122 and 124 are equal to each other. That is, if there is a difference between the flow-through abilities of the front-side passage 122 and the rear-side passage 124, a pressure difference between the exhaust gas flowing in the front-side passage 122 and the exhaust gas flowing in the rear-side passage 124 is generated. The pressure difference between the exhaust gases causes an exhaust resistance difference between the exhaust gas discharged from the cylinders 10a and 10d and the exhaust gas discharged from the cylinders 10b and 10c, so that the operating states of the cylinders 10a and 10d are different from those of the cylinders 10b and 10c. Eventually, there is a concern that the intake and exhaust characteristics of the engine 100 may deteriorate. Accordingly, it is necessary to make the flow-through abilities of the front-side passage 122 and the rear-side passage 124 equal to each other in the twin scroll turbocharger 130.
For this reason, in the twin scroll turbocharger in the related art, two exhaust gas passages are formed to be symmetrical with respect to a partition wall perpendicular to a turbine shaft as shown in, for example, FIG. 4 of PTL 1 so that the flow-through abilities of the two exhaust gas passages are equal to each other.